Organic light-emitting display device and method of manufacturing the same

ABSTRACT

An organic light-emitting display device, which may be configured to prevent moisture or oxygen from penetrating the organic light-emitting display device from the outside is disclosed. An organic light-emitting display device, which is easily applied to a large display device and/or may be easily mass produced is further disclosed. Additionally disclosed is a method of manufacturing an organic light-emitting display device. An organic light-emitting display device may include, for example, a thin-film transistor (TFT) including a gate electrode, an active layer insulated from the gate electrode, source and drain electrodes insulated from the gate electrode and contacting the active layer and an insulating layer disposed between the source and drain electrodes and the active layer; and an organic light-emitting diode electrically connected to the TFT. The insulating layer may include, for example, a first insulating layer contacting the active layer; and a second insulating layer formed of a metal oxide and disposed on the first insulating layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57. Forexample, this application is a divisional application of U.S.application Ser. No. 14/010,164 filed Aug. 26, 2013, now U.S. Pat. No.9,105,862, which is a continuation of U.S. patent application Ser. No.13/678,256 filed Nov. 15, 2012, now U.S. Pat. No. 8,546,175, which is adivisional of U.S. patent application Ser. No. 12/829,139 filed Jul. 1,2010, now U.S. Pat. No. 8,330,150, which claims the benefit of KoreanPatent Application No. 10-2009-0102282, filed on Oct. 27, 2009, in theKorean Intellectual Property Office, the disclosure of each of which isincorporated herein in its entirety by reference.

BACKGROUND

The present invention relates to an organic light-emitting displaydevice including a thin-film transistor (TFT) and a method ofmanufacturing the same.

Description of the Related Art

An active matrix type organic light-emitting display device includes athin-film transistor (TFT), and an organic light-emitting diodeconnected to the TFT in each pixel. An active layer of the TFT is formedof amorphous silicon or polysilicon. Recently, there have also beenattempts to use an oxide semiconductor to form the active layer.Properties, such as a threshold voltage and an S-factor, of the oxidesemiconductor, however, can easily change due to moisture or oxygen thatpenetrates the organic light-emitting display device from the outside.Such a change of the threshold voltage due to moisture or oxygen isaccelerated by a direct current (DC) bias of a gate electrode whiledriving the TFT. Thus, DC stability is an important factor when usingthe oxide semiconductor.

To strengthen barrier characteristics of the oxide semiconductor againstmoisture or oxygen, an aluminum oxide (AlO_(x)) layer or a titaniumnitride (TiN) layer may be applied to a substrate, but since the AlO_(x)or TiN layer is prepared by using a reactive sputtering method or anatomic layer deposition (ALD) method, it is difficult to apply theAlO_(x) or TiN layer to a large substrate and its mass productivity islow.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

Some aspects of the present disclosure relate to an organiclight-emitting display device including a thin-film transistor (TFT)configured to prevent moisture or oxygen from penetrating the organiclight-emitting display device from the outside. Other aspects of thepresent disclosure relate to a method of manufacturing an organiclight-emitting display device.

In one aspect, an organic light-emitting display device may be easilyapplied to a large display device.

In another aspect, an organic light-emitting display device may beeasily mass produced.

In another aspect a method of manufacturing the organic light-emittingdisplay device is disclosed.

In another aspect, an organic light-emitting display device includes,for example, a thin-film transistor (TFT) comprising a gate electrode,an active layer insulated from the gate electrode, source and drainelectrodes insulated from the gate electrode and contacting the activelayer, and an insulating layer formed between the source and drainelectrodes and the active layer and an organic light-emitting diodeelectrically connected to the TFT.

In some embodiments, the insulating layer includes, for example, a firstinsulating layer contacting the active layer and a second insulatinglayer substantially formed from a metal oxide and formed on the firstinsulating layer. In some embodiments, the second insulating layer has agradient of metal content with respect to its thickness. In someembodiments, the metal content decreases toward the first insulatinglayer. In some embodiments, the metal is substantially formed fromaluminum, titanium, or an alloy thereof. In some embodiments, theinsulating layer further comprises a third insulating layersubstantially formed from a metal oxide or a metal nitride and formed onthe second insulating layer. In some embodiments, the insulating layerfurther comprises a fourth insulating layer formed on the thirdinsulating layer. In some embodiments, the third insulating layer issubstantially formed from aluminum oxide, aluminum nitride, titaniumoxide or titanium nitride. In some embodiments, a metal layer is formedbetween the second insulating layer and the third insulating layer. Insome embodiments, the metal layer is substantially formed from aluminum,titanium or an alloy thereof. In some embodiments, the active layer issubstantially formed from an oxide semiconductor. In some embodiments,the first insulating layer is substantially formed from silicon oxide.

In another aspect, a method of manufacturing an organic light-emittingdisplay device includes, for example, forming a gate electrode on asubstrate; forming a gate insulating layer covering the gate electrodeon the substrate; forming an active layer on the gate insulating layer;forming an insulating layer covering a channel region of the activelayer; forming source and drain electrodes contacting the active layerand formed on the insulating layer and forming an organic light-emittingdiode to be electrically connected to one of the source and drainelectrodes.

In some embodiments, the forming of the insulating layer includes, forexample, forming a first insulating layer covering the channel region ofthe active layer and forming a second insulating layer from a metaloxide on the first insulating layer. In some embodiments, the forming ofthe second insulating layer includes, for example, forming a metal layeron the first insulating layer and thermal-processing at least the metallayer so as to form a part of the metal layer contacting the firstinsulating layer as a metal oxide. In some embodiments, the secondinsulating layer has a gradient of metal content with respect to itsthickness. In some embodiments, the metal content decreases toward thefirst insulating layer. In some embodiments, the metal is substantiallyformed from aluminum, titanium or an alloy thereof. In some embodiments,the method further includes, for example, forming a third insulatinglayer is substantially formed of a metal oxide or a metal nitride on thesecond insulating layer. In some embodiments, the forming of the thirdinsulating layer includes, for example, forming a metal layer on thefirst insulating layer and forming a part of the metal layer as thethird insulating layer by oxidizing or nitrifying a surface of the metallayer opposite of the first insulating layer. In some embodiments, themethod further includes, for example, forming a fourth insulating layeron the third insulating layer. In some embodiments, the third insulatinglayer is substantially formed from aluminum oxide, aluminum nitride,titanium oxide or titanium nitride. In some embodiments, a metal layeris formed between the second insulating layer and the third insulatinglayer. In some embodiments, the metal layer is substantially formed fromaluminum, titanium or an alloy thereof. In some embodiments, the activelayer is substantially formed of an oxide semiconductor. In someembodiments, the first insulating layer is substantially formed ofsilicon oxide.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of the present disclosure will become more fully apparent fromthe following description and appended claims, taken in conjunction withthe accompanying drawings. It will be understood these drawings depictonly certain embodiments in accordance with the disclosure and,therefore, are not to be considered limiting of its scope; thedisclosure will be described with additional specificity and detailthrough use of the accompanying drawings. An apparatus according to someof the described embodiments can have several aspects, no single one ofwhich necessarily is solely responsible for the desirable attributes ofthe apparatus. After considering this discussion, and particularly afterreading the section entitled “Detailed Description of Certain InventiveEmbodiments” one will understand how illustrated features serve toexplain certain principles of the present disclosure.

FIG. 1 is a cross-sectional view schematically illustrating an organiclight-emitting display device according to an embodiment of the presentdisclosure.

FIG. 2 is a cross-sectional view of a portion A of FIG. 1, according toan embodiment of the present disclosure.

FIG. 3 is a cross-sectional view of a portion A of FIG. 1, according toanother embodiment of the present disclosure.

FIG. 4 is a cross-sectional view of a portion A of FIG. 1, according toanother embodiment of the present disclosure.

FIG. 5 is a cross-sectional view of a portion A of FIG. 1, according toanother embodiment of the present disclosure.

FIGS. 6A through 6E are cross-sectional views for describing a method ofmanufacturing an insulating layer of FIG. 2, according to an embodimentof the present disclosure.

FIGS. 7A through 7E are cross-sectional views for describing a method ofmanufacturing an insulating layer of FIG. 4, according to anotherembodiment of the present disclosure.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

In the following detailed description, only certain exemplaryembodiments have been shown and described, simply by way ofillustration. As those skilled in the art would realize, the describedembodiments may be modified in various different ways, all withoutdeparting from the spirit or scope of the present disclosure. Further,in several exemplary embodiments, constituent elements having the sameconstruction are assigned the same reference numerals and arerepresentatively described in connection with a first exemplaryembodiment. In the remaining exemplary embodiments, constituent elementsdifferent from those of the first exemplary embodiment are described. Toclarify the description of the exemplary embodiments, the same referencenumbers will be used throughout the drawings to refer to the same orlike parts. Further, the size and thickness of each of the elementsshown in the drawings are arbitrarily shown for better understanding andease of description, and the embodiments are not limited thereto.

In addition, in the drawings, the thickness of layers, films, panels,regions, etc., are exaggerated for clarity. The thickness of the layers,films, panels, regions, etc., is enlarged in the drawings for betterunderstanding and ease of description. Accordingly, the drawings anddescription are to be regarded as illustrative in nature and notrestrictive. It will be understood that when an element such as a layer,film, region, or substrate is referred to as being “on” another element,it can be directly on the other element or intervening elements may alsobe interposed therebetween. Also, when an element is referred to asbeing “connected to” another element, it can be directly connected tothe other element or be indirectly connected to the other element withone or more intervening elements interposed therebetween.

FIG. 1 is a cross-sectional view schematically illustrating an organiclight-emitting display device according to an embodiment of the presentdisclosure. Referring to FIG. 1, a thin-film transistor (TFT) 2 and anorganic light-emitting diode 3 are disposed on a substrate 1. FIG. 1 isa part of one pixel of the organic light-emitting display device, andthe organic light-emitting display device includes a plurality ofpixels. The TFT 2 may include a gate electrode 21 formed on thesubstrate 1, a gate insulating layer 22 covering the gate electrode 21,an active layer 23 formed on the gate insulating layer 22, an insulatinglayer 24 formed on the gate insulating layer 22 to cover the activelayer 23, and source and drain electrodes 25 and 26 contacting theactive layer 23 and disposed on the insulating layer 24. The TFT 2 ofFIG. 1 has a bottom gate structure; however the structure of the TFT 2is not limited thereto, and may be a top gate structure.

A buffer layer (not shown) may be formed on the substrate 1, wherein thebuffer layer is formed of an inorganic material, such as silicon oxide.The gate electrode 21 formed on the substrate 1 may include a singlelayer or a plurality of layers formed of conductive metal. The gateelectrode 21 may include molybdenum. The gate insulating layer 22 may beformed of silicon oxide, tantalum oxide, or aluminum oxide, but amaterial for forming the gate insulating layer 22 is not limitedthereto. The active layer 23 is formed on the gate insulating layer 22by using a patterning method. The active layer 23 may be formed of anoxide semiconductor. For example, the active layer 23 may be agallium-indium-zinc-oxide (G-I-Z-O) layer, such as an(In₂O₃)a(Ga₂O₃)b(ZnO)c layer, wherein a, b, and c are each independentlya real number, and wherein a≧0, b≧0, and c>0.

The insulating layer 24 is formed to cover the active layer 23. Theinsulating layer 24 may also be formed to protect a channel region 23 aof the active layer 23 and, as shown in FIG. 1, the insulating layer 24may be formed to cover the entire active layer 23, excluding regionscontacting the source and drain electrodes 25 and 26. Thus, as depictedin FIG. 1 the insulating layer 24 is formed on the active layer 23 andalso extends between a passivation layer 27 (discussed further below)and the gate insulating layer 22 on either side of the active layer 23.A location where the insulating layer 24 is formed is not limited to thediscussion above or to the embodiment of FIG. 1. For example, theinsulating layer 24 may be formed only on the channel region 23 a of theactive layer 23.

The source electrode 25 and the drain electrode 26 that are formed onthe insulating layer 24 are configured to contact the active layer 23. Apassivation layer 27 may be formed on the insulating layer 24 to coverthe source and drain electrodes 25 and 26. A first electrode 31 of theorganic light-emitting diode 3 may be formed on the passivation layer 27and may contact the drain electrode 26 by forming a via-hole 29 in thepassivation layer 27. A pixel defining layer 28 exposing a part of thefirst electrode 31 is formed on the passivation layer 27, and an organiclayer 32 and a second electrode 33 are formed on the first electrode 31exposed by the pixel defining layer 28. The first electrode 31 may bepatterned according to each pixel.

When the organic light-emitting display device is a top-emissive typerealizing an image toward the second electrode 33, the first electrode31 may be a reflective electrode. Accordingly, the first electrode 31may include a reflective layer formed of an alloy including aluminum(Al), silver (Ag), or the like. When the first electrode 31 is an anode,the first electrode 31 may be formed of a metal oxide having a highabsolute value of work function, such as indium tin oxide (ITO), indiumzinc oxide (IZO), indium oxide (In₂O₃) or zinc oxide (ZnO). On the otherhand, when the first electrode 31 is a cathode, the first electrode 31may be formed of a high conductive metal having a low absolute value ofwork function, such as Ag, magnesium (Mg), Al, platinum (Pt), palladium(Pd), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium(Cr), lithium (Li) or calcium (Ca). Accordingly, when the firstelectrode 31 is a cathode, the first electrode 31 may not include areflective layer.

The second electrode 33 may be a transmissive electrode. Accordingly,the second electrode 33 may include a thin semi-transmissive reflectivelayer formed of Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, or Ca or atransmissive metal oxide, such as ITO, IZO or ZnO. When the firstelectrode 31 is an anode, the second electrode 33 is a cathode and whenthe first electrode 31 is a cathode, the second electrode 33 is ananode. The organic layer 32 disposed between the first electrode 31 andthe second electrode 33 may include one or more of a hole injectionlayer, a hole transport layer, an emission layer, an electron injectionlayer, and an electron transport layer. Here, in the embodiment of FIG.1 the emission layer is included. Although not illustrated in FIG. 1, aprotective layer may be formed on the second electrode 33 and theorganic light-emitting display device may be sealed by using glass.

The insulating layer 24 may be formed as shown in FIG. 2. FIG. 2 is across-sectional view of a region “A” of FIG. 1, according to anembodiment of the present disclosure. Referring to FIG. 2, theinsulating layer 24 includes a first insulating layer 242 contacting theactive layer 23, a second insulating layer 244 disposed on the firstinsulating layer 242, a third insulating layer 246 disposed on thesecond insulating layer 244 and a fourth insulating layer 248 disposedon the third insulating layer 246. The first insulating layer 242 mayinclude, for example, an oxide layer formed of silicon oxide (SiO_(x))using a plasma enhanced chemical vapor deposition (PECVD) method or asputtering method. As will be described later, the first insulatinglayer 242 may protect the active layer 23 from being contaminated whileforming a metal layer and may diffuse a metal according to a laterthermal-process.

The second insulating layer 244 may be formed of a metal oxide and mayhave a gradient of metal content with respect to a thickness thereof.Here, the metal content of the second insulating layer 244 may decreasemoving in a direction toward the first insulating layer 242.Accordingly, the metal content of the second insulating layer 244 is thehighest near the third insulating layer 246 and the lowest near thefirst insulating layer 242. The metal of the second insulating layer 244may include, for example, aluminum, titanium or an alloy thereof.Accordingly, the content of aluminum or titanium may be diffused insilicon oxide to have the concentration gradient according to thethickness of the second insulating layer 244. The third insulating layer246 may be formed of metal oxide or metal nitride, for example, aluminumoxide, aluminum nitride, titanium oxide or titanium nitride. The fourthinsulating layer 248 disposed on the third insulating layer 246 may beformed of silicon oxide, for example, like the first insulating layer242.

As described above, the insulating layer 24 may have a stacked structureincluding the first insulating layer 242 through the fourth insulatinglayer 248 and may thus have a higher barrier effect with respect to theactive layer 23 compared to a conventional insulating layer formed of asingle layer of silicon oxide or silicon nitride. Accordingly, theinsulating layer 24 may sufficiently protect the active layer 23 frommoisture or oxygen. Also, as will be described later, a method offorming the first through fourth insulating layers 242 through 248 maybe simple, and thus the insulating layer 24 may be easily applied to alarge display.

FIG. 3 is a cross-sectional view of the portion A of FIG. 1, accordingto another embodiment of the present disclosure. Referring to FIG. 3,the fourth insulating layer 248 is omitted from the insulating layer 24of FIG. 2. The fourth insulating layer 248 may not be formed if theinsulating layer 24 has a sufficient barrier effect by stacking thefirst through third insulating layers 242 through 246.

FIG. 4 is a cross-sectional view of the portion A of FIG. 1, accordingto another embodiment of the present disclosure. Referring to FIG. 4,the insulating layer 24 further includes a metal layer 245 between thesecond insulating layer 244 and the third insulating layer 246 of FIG.2. The metal layer 245 may be formed of aluminum, titanium or an alloythereof. By disposing the metal layer 245, the barrier characteristicsof the insulating layer 24 may be increased. Although not illustrated indetail, the metal layer 245 may not be formed contacting the source anddrain electrodes 25 and 26 of FIG. 1, by oxidizing or nitrifying theends of the metal layer 245 while oxidizing or nitrifying the metallayer 245.

FIG. 5 is a cross-sectional view of the portion A of FIG. 1, accordingto another embodiment of the present disclosure. Referring to FIG. 5,the insulating layer 24 further includes the metal layer 245 between thesecond insulating layer 244 and the third insulating layer 246 of FIG.3. Details about the metal layer 245 are as described above with respectto FIG. 4. Although not illustrated in detail, if the metal layer 245has a thickness to be diffused only to the first insulating layer 242,the insulating layer 24 may only include the first and second insulatinglayers 242 and 244.

A method of manufacturing the insulating layer 24 will now be describedin detail. FIGS. 6A through 6E are cross-sectional views for describinga method of manufacturing the insulating layer 24 of FIG. 2. First,referring to FIG. 6A, the first insulating layer 242 is formed to coverthe active layer 23 that is patterned as described with reference toFIG. 1. The first insulating layer 242 may be formed of silicon oxideusing a PECVD method or a sputtering method. As described above, thefirst insulating layer 242 is configured to protect the active layer 23from being contaminated while forming the metal layer 245, and alsoconfigured to diffuse a metal according to a later thermal-process.

Then, referring to FIG. 6B, the metal layer 245 is formed on the firstinsulating layer 242. The metal layer 245 is formed of aluminum,titanium or an alloy thereof because an oxide or nitride layer of thealuminum or titanium is hard. The thickness of the metal layer 245 maybe about 50 Å, but is not limited thereto.

Next, as shown in FIG. 6C, the top of the metal layer 245 is convertedto the third insulating layer 246. The third insulating layer 246 isformed by forming a metal oxide by thermal-processing the metal layer245 under an oxygen atmosphere, or by forming a metal nitride byplasma-processing the metal layer 245 under a nitrogen atmosphere. Indetail, the third insulating layer 246 may be formed of AlO_(x) or TiNhaving excellent barrier characteristics, and the thickness of the thirdinsulating layer 246 may be about 20 Å from the top of the metal layer245. Here, when an additional thermal-process is performed at atemperature of about 250 Å to about 350 Å, the metal of the metal layer245 diffuses into the oxide of the first insulating layer 242, and thusthe top of the first insulating layer 242 and the metal layer 245 changeto the second insulating layer 244 formed of metal oxide having agradient of metal content, as shown in FIG. 6D. As a result, the metallayer 245 that was purely formed of the metal disappears and threelayers, namely, the first through third insulating layers 242 through246, are formed. The second insulating layer 244 may be formed byperforming the thermal-process before forming the third insulating layer246 through nitrification or oxidization. Further, the third insulatinglayer 246 may not be formed during nitrification or oxidization.

Then, in order to increase the thickness or productivity of theinsulating layer 24, the fourth insulating layer 248 may be selectivelyformed on the third insulating layer 246 by using silicon oxide via aPECVD method or a sputtering method, as shown in FIG. 6E. As describedabove, since the insulating layer 24 formed of AlO_(x) or TiN havingexcellent barrier characteristics is not formed by using a reactivesputtering method or an atomic layer deposition (ALD) method, theinsulating layer 24 may be easily applied to a large substrate and mayeasily be mass produced.

FIGS. 7A through 7E are cross-sectional views for describing a method ofmanufacturing the insulating layer 24 of FIG. 4, according to anotherembodiment of the present invention. In the method of FIGS. 7A through7E, the processes shown in FIGS. 7A through 7C are identicalrespectively to the processes described with reference to FIGS. 6Athrough 6C. In FIG. 7D, while forming the second insulating layer 244 bythermal-processing the metal layer 245, a part of the metal layer 245 isremained, instead of diffusing all of the metal layer 245 into the firstinsulating layer 242, so that the metal layer 245 is disposed betweenthe second insulating layer 244 and the third insulating layer 246.Accordingly, the insulating layer 24 has a four-layered structure. Then,to increase the thickness or productivity, the fourth insulating layer248 may be selectively formed on the third insulating layer 246 by usingsilicon oxide via a PECVD method or a sputtering method, as shown inFIG. 7E. An insulating layer may be used to increase a barrier effectwith respect to an active layer, and thus may sufficiently protect theactive layer from moisture or oxygen. Also, since the insulating layerformed of AlO_(x) or TiN having excellent barrier characteristics is notmanufactured by using a reactive sputtering method or an ALD method, theinsulating layer may be easily applied to a large substrate and may beeasily mass produced.

It will be appreciated by those skilled in the art that variousmodifications and changes may be made without departing from the scopeof the present disclosure. It will also be appreciated by those of skillin the art that parts included in one embodiment are interchangeablewith other embodiments; one or more parts from a depicted embodiment canbe included with other depicted embodiments in any combination. Forexample, any of the various components described herein and/or depictedin the Figures may be combined, interchanged or excluded from otherembodiments. With respect to the use of substantially any plural and/orsingular terms herein, those having skill in the art can translate fromthe plural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity. Further, while the present disclosure has described certainexemplary embodiments, it is to be understood that the scope of thedisclosure is not limited to the disclosed embodiments, but, on thecontrary, is intended to cover various modifications and equivalentarrangements included within the spirit and scope of the appended claimsand equivalents thereof.

What is claimed is:
 1. A method of manufacturing an organiclight-emitting display device, the method comprising: forming a gateelectrode on a substrate; forming a gate insulating layer covering thegate electrode on the substrate; forming an active layer on the gateinsulating layer; forming an insulating layer covering a channel regionof the active layer; forming source and drain electrodes contacting theactive layer and formed on the insulating layer; and forming an organiclight-emitting diode to be electrically connected to one of the sourceand drain electrodes, wherein the forming of the insulating layercomprises: forming a first insulating layer covering the channel regionof the active layer; and forming a second insulating layer substantiallycomprising a metal oxide on the first insulating layer, wherein theforming of the second insulating layer comprises: forming a metal layeron the first insulating layer; and thermal-processing at least the metallayer so as to form a part of the metal layer contacting the firstinsulating layer as a metal oxide.
 2. The method of claim 1, wherein thesecond insulating layer has a gradient of metal content with respect toits thickness.
 3. The method of claim 2, wherein the metal contentdecreases toward the first insulating layer.
 4. The method of claim 2,wherein the metal substantially comprises aluminum, titanium or an alloythereof.
 5. The method of claim 1, further comprising forming a thirdinsulating layer substantially comprises a metal oxide or a metalnitride on the second insulating layer.
 6. The method of claim 5,wherein the forming of the third insulating layer comprises: forming ametal layer on the first insulating layer; and forming a part of themetal layer as the third insulating layer by oxidizing or nitrifying asurface of the metal layer opposite of the first insulating layer. 7.The method of claim 5 further comprising forming a fourth insulatinglayer on the third insulating layer.
 8. The method of claim 5, whereinthe third insulating layer substantially comprises aluminum oxide,aluminum nitride, titanium oxide or titanium nitride.
 9. The method ofclaim 5, wherein a metal layer is formed between the second insulatinglayer and the third insulating layer.
 10. The method of claim 9, whereinthe metal layer substantially comprises aluminum, titanium or an alloythereof.
 11. The method of claim 1, wherein the active layersubstantially comprises an oxide semiconductor.
 12. The method of claim1, wherein the first insulating layer substantially comprises siliconoxide.